Organic Rankine Cycle (ORC) systems enable locally emission-free power generation. Nevertheless, they cause emissions and resource consumption during their life cycle. Life cycle assessment (LCA) according to ISO 14044 allows identification of key environmental impacts caused by a product. An LCA was carried out for a direct air-cooled ORC system applied to recover waste heat. As working fluid R-245fa was considered and the nominal generator output was set to 100 kW_el . A volumetric expander with a fixed volume ratio was assumed. The simplified thermodynamic cycle was modelled for a source temperature of 130 °C. On this basis, commercially available components were selected according to publicly available data. The inventory analysis was carried out with simple mass fraction inventory of the mainly used materials. Subsequently, the reduced manufacturing processes were implemented using the integrated database of the LCA software GaBi Education. Scenarios were defined for the lifetime of the system and full load operation hours per year, which resulted in different amounts of electricity provided by the system. The life cycle impact assessment was carried out using the ReCiPe 2016 method, including 18 impact categories. Results for each scenario were calculated for the entire system and all results were standardized related to the functional unit of kWh_el . Three substantial results were derived. First, the greenhouse gas emissions of the ORC system were significantly increased due to the unavoidable losses of R-245fa during the life cycle. These emissions of the working fluid significantly exceeded those from manufacturing of the system. Second, environmental impacts such as climate change, ionizing radiation, terrestrial acidification, water usage, and fine particulate matter formation were found to be higher compared to electricity generation by wind power if the full load operation hours remain low. Third, a reduction of environmental impacts could be achieved if low global warming potential fluids are used, resource-saving production processes are chosen, a hermetic design is implemented, and full-load operation hours are increased.